1. Field of the Invention
This invention relates to a catheter used to improve blood flow to a patient's heart, and more particularly to a catheter with an ultrasound transducer that creates revascularization channels and/or stimulates angiogenesis in a patient's heart.
2. Description of Related Art
Cardiovascular diseases are generally characterized by an impaired supply of blood to the heart or other target organs. Myocardial infarction (MI), commonly referred to as heart attacks, are a leading cause of mortality.
The number and variety of medical methods available to repair the effects of cardiovascular disease has increased rapidly over the last several years. More particularly, alternatives to open heart surgery and cardiovascular by-pass surgery have been extensively investigated, resulting in non-surgical procedures such as percutaneous transluminal coronary angioplasty, laser angioplasty and atherectomy. These procedures are primarily directed toward the reduction of stenosis within the vasculature of a patient by either expanding the lumen through the use of a balloon, or ablating or otherwise removing the material making up the stenosis.
While these procedures have shown considerable promise, many patients still require bypass surgery due to such conditions as the presence of extremely diffuse stenotic lesions, the presence of total occlusions and the presence of stenotic lesions in extremely tortuous vessels. Also, some patients are too sick to successfully undergo bypass surgery, and because the above treatments require surgical backup in the case of complications, they are untreatable. Some patients requiring repeat bypass surgeries are also untreatable.
Another method of improving myocardial blood supply is transmyocardial revascularzation (TMR) where channels are formed from the epicardial to the endocardial portions of the heart. TMR relieves ischemia by allowing blood to pass from the ventricle through the channels either directly into other vessels perforated by the channels or into myocardial sinusoids which connect to the myocardial microcirculation. In one method of TMR a CO.sub.2 laser is used to produce channels in the ventricle from the epicardium through a portion of the myocardium. This procedure follows a surgical cutdown. External pressure is used to stop bleeding from the ventricle to the outside. The channel is sealed at the epicardial layer. However, the channel's patency in the endocardial and myocardial layers remains questionable. Lasers are an expensive energy source and may be problematic in producing acceptable volumetric tissue ablation rates. RF energy has also been disclosed as an energy source for TMR. A high frequency voltage delivered from an RF electrode is applied to ablate or disintegrate tissue at the heart wall. The RF electrode is axially translated towards the ventricular wall to form a revascularizing channel or artificial vessel from the ventricle to the myocardium in order to increase blood flow. RF electrodes can create very high temperatures which can create an undesired depth of cell necrosis.
A need exists for a cost effective method to increase blood flow to a patient's heart. Another need exists for a method using a cost effective energy source to create revascularzation channels and/or stimulate angiogenesis. Yet another need exists for a method using an ultrasound energy device to improve blood flow to a patient's heart.